As a gear transmission device configured as above, Patent Document 1 discloses a technique having a non-uniform rotation face gear and a pinion gear that meshes with this face gear. According to the above technique, the pinion gear is driven by an electric motor and the non-uniform rotation face gear is operably coupled with a steering mechanism of a steering system.
The steering system disclosed in this Patent Document 1 is configured such that a pressure angle formed between the non-uniform rotation face gear and the pinion gear is smaller in a region where a large torque is required than a region where a small torque is effective. Further, with the non-uniform rotation face gear, there is provided an arrangement that by varying a distance from the center of the gear to a region where a tooth face is formed, a steering gear characteristics is realized.
Patent Document 2 discloses a technique according to which a clutch device is operated via an input gear driven by an electric motor and a face gear meshing therewith. The face gear has a fan-like shape and teeth portions formed only at a region thereof corresponding to the arc of the fan-shape.
In this Patent Document 2, as one end of a rod for operating the clutch device is supported to the face gear, there is realized engagement/disengagement of the clutch device in association with a pivotal movement of the face gear.